1. Field of the Invention:
The invention relates to an improved inflatable well tool, such as a packer or a bridge plug, for use in a subterranean well, and a method of using same.
2.Brief Description of the Prior Art:
Inflatable packers or bridge plugs have long been utilized in subterranean wells. Such inflatable tools normally comprise an elastomeric sleeve element mounted in surrounding relationship to a tubular body portion. Pressured fluid is communicated from the top of the well or interior of the well bore to the bore of the tubular body and thence through radial passages to the interior of an inner elastomeric sleeve. Such inner elastomeric sleeve may be surrounded and secured relative to a reinforcing sheath, which may be provided in the form of a plurality of peripherally overlapping, slats or ribs. Such reinforcing sheath may be formed of longitudinally extending strips which are of a suitable length so that they generally extend beyond each of the ends of the inflatable well tool with each of the longitudinally extending strips circumferentially overlapping an adjacent strip. The width of such strips and their arrangement in forming such a sheath is such that each of the strips will overlap the next adjacent strip when the inflatable member is deflated and each strip will overlap the next adjacent strip when the inflatable member is inflated, thus forming a reinforcing sheath for the inflatable element at all times.
Depending upon the use for which the inflatable member is constructed, the base material of the reinforcing sheath may be of flat braided wire impregnated with elastomer or plastic, strips of plain woven fiberglass which may or may not be impregnated with elastomer or plastic, strips of plain or woven nylon, strips of spring steel, strips of metal such as ordinary mild steel or other permanently deformable material, strips of other plain or woven material, such as teflon or other plastics, depending upon the pressure to which the inflatable member is to be inflated.
The exterior of the reinforcing sheath is either partially or completely surrounded and bonded to an outer annular elastomeric packing element of substantially greater wall thickness. Normally, an upper securing assembly wedgingly engages the upper end of the inner elastomeric sleeve with the reinforcing slats and are fixedly and sealably secured relative to the central tubular body, while a lower securing assembly is sealably secured to a sealing sub which is mounted for slidable and sealable movements on the exterior of the central tubular body, in response to the inflation forces. Such structures of this general type are shown in U.S. Pat. Nos. 3,160,211; 3,604,732; and 3,837,947.
With inflatable tools of this type, it has been observed that the upper end of the reinforced inner elastomeric sleeve was expanding prior to expansion of the packing element and becoming deformed, resulting in high local stresses. Such deformation occurs because the ends of the inner elastomeric sleeve element expand with much less pressure than the medial portions of such sleeve element which are reinforced against expansion by the thick walled elastomeric packing sleeve. Such premature expansion of the upper end of the inflatable elements of the prior art inflatable packers resulted in an inward movement of the opposite end of the elastomeric cover sleeve, forcing the inner elastomeric sleeve into sealing relationship with the exterior of the tubular central body and thus preventing passage of the pressured fluid employed for expanding the inflatable inner elastomeric sleeve from reaching the lower portions of such sleeve.
Another reason for the premature expansion of the upper end of the inner elastomeric sleeve of the inflatable packing assembly lies in the fact that any inflation movement of the lower portions of the inflatable elements results in an immediate axial displacement of the lower securing assembly relative to the stationary tubular central body. Thus, the stress in the lower portions of the packing assembly is substantially relieved by such axial movement, while the fluid pressure works on the upper portion of the inner elastomeric sleeve to deform it radially outwardly.
It has been observed that both the upper end and lower end portions of the inner sleeve expand prior to the medial portions, thus causing fluid to be trapped around the cover sleeve and between the well conduit and the casing C or uncased well bore. Subsequent leakage of such trapped fluid will permit the cover to expand, reducing the inflation pressure and setting the stage for fluid leakage past the cover element.
In U.S. Pat. No. 4,832,120, there is shown and disclosed an inflatable tool for single set within a subterranean well which incorporates one solution to this general problem. In such patent, the lower end of the inflatable packer is shear-pinned to the tubular body such that the shearable means will not release and cause the outer assembly portion of the tool which carries with it the packing component to contract relative to the tubular body until such time as a pre-determined pressure within the inflatable element is reached, thereby assuring that there is a uniform radial inflation of the inflatable element, thus overcoming the problems described above. However, such a device is not completely satisfactory for incorporation into a resettable inflatable tool, which is intended to be activated, deactivated, and reactivated a number of times during one trip of a conduit within a subterranean well, such as during the performance of remedial operations, such as acidizing and other stimulation techniques. In such resettable tools, the integrity of the inflation process of the inflatable element cannot be repeated.
The present invention addresses the problems set forth above, which occur in a well tool which is intended to be set, unset and reset within a well during one trip of the conduit carrying such tool into the well. In the case of a resettable tool, once the resettable tool has been released and moved to a new location in the hole, if the deflated element is not pulled down to the initial run-in position, it may be free to swab up and possibly prevent downward movement of the tool resulting in severe damage to the inflatable element and other components of the tool.
The present invention addresses the problems set forth above which occur in a resettable tool which can be run into the well, set, unset, and reset, all in one trip of the conduit carrying the tool into the well. The present invention also permits tension to be applied through the inflatable element to further assist in proper re-setting action.